Engine control device

ABSTRACT

A control device for an engine is provided. A cavity formed in a crown surface of a piston of the engine includes a first cavity part disposed in a radially center area, a second cavity part disposed radially outward of the first cavity part, and a connecting part connecting these two parts. The control device causes a fuel injection valve to perform a first injection in which fuel is injected at a timing when the piston is located at an advancing side of CTDC and an injection axis thereof intersects with the connecting part, a second injection in which fuel is injected toward the first cavity part at a retarding side of the first injection, and a middle injection in which fuel is injected at a timing between the first and second injections, for a period shorter than each of the first and second injections.

TECHNICAL FIELD

The present disclosure relates to a control device for an engine where apart of a combustion chamber is formed by a piston provided with acavity.

BACKGROUND OF THE DISCLOSURE

A combustion chamber of an engine for vehicles, such as automobiles, isdefined by an inner wall surface of a cylinder, a bottom surface of acylinder head (a ceiling surface of the combustion chamber), and a crownsurface of a piston. Fuel is supplied to the combustion chamber from afuel injection valve. A fuel injection control is known, in which acavity is disposed in the crown surface of the piston, and fuel isinjected from the fuel injection valve toward the cavity. JP2007-211644Adiscloses a control method in which the cavity has a two-step structurecomprised of an upper cavity and a lower cavity, and fuel is injected toa lip part located in the middle of the cavities.

An ideal mode of combustion inside the combustion chamber is to causecombustion in which air existing inside the combustion chamber is usedup. Yet, inside the combustion chamber of which a bottom surface isdefined by the piston crown surface having the upper and lower 2-stepcavities, no useful technique has been proposed for a control mode ofthe fuel injection for effectively using the air (oxygen) existinginside the combustion chamber.

SUMMARY OF THE DISCLOSURE

One purpose of the present disclosure is to provide a control device foran engine where a part of a combustion chamber is defined by a pistoncrown surface having upper and lower 2-step cavities, which is capableof effectively using oxygen existing inside the combustion chamber.

According to one aspect of the present disclosure, a control device foran engine including a combustion chamber formed by a cylinder, a crownsurface of a piston, and a ceiling surface, and a fuel injection valvedisposed in a radially center part of the ceiling surface and configuredto inject fuel into the combustion chamber, is provided. A cavity isformed in the crown surface of the piston, and the cavity includes afirst cavity part disposed in a radially center area of the crownsurface and provided with a first bottom part having a first depth in acylinder axis direction, a second cavity part disposed in the crownsurface at a location radially outward of the first cavity part andprovided with a second bottom part having a second depth shallower thanthe first depth in a cylinder axis direction, and a connecting partconnecting the first cavity part with the second cavity part. Thecontrol device includes a processor configured to execute a fuelinjection controlling module to control operation of the fuel injectionvalve. The fuel injection controlling module causes the fuel injectionvalve to perform a first injection in which fuel is injected at a timingwhen the piston is located at an advancing side of a compression topdead center, and an injection axis of the fuel injection valveintersects with the connecting part of the cavity, a second injection inwhich fuel is injected toward the first cavity part at a retarding sideof the first injection, and a middle injection in which fuel is injectedat a timing between the first injection and the second injection, for aninjection period shorter than each of the first injection and the secondinjection.

According to this configuration, the fuel injected by the firstinjection at the timing when the injection axis intersects with theconnecting part is directed toward the connecting part, enters the firstand second cavity parts, and is mixed with air (oxygen) in the cavityparts to form a mixture gas, thereby resulting in combustion. Moreover,the fuel injected by the second injection which is performed at theretarded timing from the first injection is mixed with air which remainsin the first cavity part to form the mixture gas, thereby resulting incombustion. Then, in the middle injection performed at the timingbetween the first injection and the second injection, the fuel isinjected during the injection period shorter than the first injectionand the second injection. It becomes difficult for the fuel injected bythe middle injection during the short injection period to reach thefirst and second cavity parts, and the fuel is mixed with airexclusively near the radial center of the combustion chamber to form themixture gas, thereby resulting in combustion. That is, in the middleinjection, oxygen in the area of the combustion chamber which is notused for the first injection and the second injection is utilizedpositively to form the mixture gas. Thus, the oxygen existing inside thecombustion chamber can effectively be utilized, and therefore, thegeneration of soot can be reduced. Moreover, since the middle injectionis performed at the timing between the first injection and the secondinjection, the combustion by the middle injection contributes to enginetorque.

The fuel injection controlling module may set the injection period sothat an injection distance of the middle injection becomes shorter thana distance between an injection hole of the fuel injection valve and awall surface of the cavity.

According to this configuration, penetration of the middle injection isset to not reach the wall surface of the cavity including the first andsecond cavity parts. Thus, the middle injection is set to an injectionmode in which air near the radial center of the combustion chamber caneasily be used.

The fuel injection controlling module may set a fuel amount injected inthe first injection larger than a fuel amount injected in the secondinjection.

The first injection utilizes both the spaces of the first and secondcavity parts as described above, whereas in the second injection, thespace of the first cavity part is exclusively utilized. According tothis configuration, in consideration of such a use of the spaces, oxygeninside the combustion chamber can efficiently be used in each injectionby setting the fuel amount in the first injection to be more than thesecond injection.

The fuel injection controlling module may set a start timing of themiddle injection at a timing closer to a start timing of the secondinjection than an end timing of the first injection.

The fuel injected by the middle injection may be caught in the fuelinjected by the second injection, if the combustion is not started bythe start timing of the second injection. In this case, it is assumedthat the fuel of the middle injection and the fuel of the secondinjection are combusted in the same area of the combustion chamber, andoxygen inside the combustion chamber is not effectively utilized.However, according to this configuration, since the middle injection canbe started at the timing close to the start timing of the secondinjection, the fuel of the middle injection is supplied to theenvironment inside the combustion chamber where the in-cylindertemperature is fully raised by the combustion by the first injection.Therefore, the fuel injected by the middle injection can be combustedimmediately, rather than being integrated into the injected fuel of thesecond injection. That is, oxygen inside the combustion chamber can beeffectively utilized.

The fuel injection controlling module may set the injection period ofthe second injection so that a start timing of the second injectionbecomes closer to the compression top dead center than an end timing ofthe second injection.

According to this configuration, the start timing of the secondinjection can be prevented from being set wastefully earlier, and thus,the combustion by the second injection can be a mode of a diffusecombustion utilizing the heat caused by the combustion of the firstinjection. Therefore, explosive power by the diffuse combustion can moreefficiently be converted to the engine torque.

The fuel injection controlling module may cause the fuel injection valveto perform the first injection and the second injection so that a firstpressure wave resulting from combustion by the first injection and asecond pressure wave resulting from combustion by the second injectionappear with a half-cycle offset.

According to this configuration, since the first pressure wave and thesecond pressure wave appear with the half-cycle offset, these pressurewaves cancel each other out. Therefore, combustion noise can be reduced.

The first cavity part may include, in a cross-section including acylinder axis, a first portion of an arc shape furthest from the fuelinjection valve, a second portion of the arc shape located between thefirst portion and the connecting part, and a third portion of the arcshape extending radially inward from the first portion. A radius ofcurvature of the arc shape may decrease from the second portion to thefirst portion, and increases from the first portion to the thirdportion.

According to this configuration, by the arc shape which is continuousfrom the first portion to the third portion, the mixture gas can flowsmoothly without stagnating in the first cavity part. That is, thein-cylinder flow from the connecting part to the first portion throughthe second portion is accelerated because the radius of the arcdecreases toward the first portion. After that, the in-cylinder flow isdecelerated at the third portion and guided radially inward. By securingthe flow in this way, the stagnation of the mixture gas in the firstcavity part can be prevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system chart of a diesel engine to which a fuel injectioncontrol device according to the present disclosure is applied.

FIG. 2A is a perspective view of a crown surface portion of a piston ofthe diesel engine illustrated in FIG. 1, and FIG. 2B is a perspectiveview illustrating a cross-section of the piston.

FIG. 3 is an enlarged view of the piston cross-section illustrated inFIG. 2B.

FIG. 4 is a view illustrating a curved surface shape of a first cavitypart, a second cavity part, and a connecting part.

FIG. 5 is a block diagram illustrating a control system for an engine.

FIG. 6 is a time chart illustrating timing of a fuel injection and arate of heat release.

FIG. 7A is a graph illustrating an interval of a peak of the rate ofheat release of combustion by a pre-injection and a main injection, andFIG. 7B is a schematic diagram illustrating a cancelation effect ofpressure waves generated by these combustion.

FIG. 8 is a graph illustrating a change in a heat release ratecharacteristic by a middle injection.

FIG. 9 is a schematic diagram illustrating start timings and end timingsof the pre-injection, the main injection, and the middle injection, andpenetrations of the injections.

FIG. 10 is a cross-sectional view of the combustion chamber,illustrating a flow state of a mixture gas in the pre-injection.

FIG. 11 is a cross-sectional view of the combustion chamber,illustrating generated areas of combustion in the pre-injection.

FIG. 12 is a cross-sectional view of the combustion chamber,illustrating a generated area of combustion in the middle injection.

FIG. 13 is a cross-sectional view of the combustion chamber,illustrating a generated area of combustion in the main injection.

FIG. 14 is a flowchart illustrating one example of a fuel injectioncontrol.

FIG. 15A is a view illustrating a peak delay of combustion resultingfrom the pre-injection, FIG. 15B is an estimation model equation of thepeak delay, and FIG. 15C is a view illustrating a calibration result ofthe estimation model equation, in a table form.

DETAILED DESCRIPTION OF THE DISCLOSURE [Overall Configuration of Engine]

Hereinafter, one embodiment of a control device for an engine accordingto the present disclosure is described in detail, with reference to theaccompanying drawings. This embodiment illustrates one example in whichthe present disclosure is applied to a control of a diesel enginesystem. First, the entire configuration of the diesel engine system isdescribed with reference to FIG. 1. The diesel engine illustrated inFIG. 1 is a four-cycle diesel engine mounted to a vehicle, as a powersource for propulsion. The diesel engine system includes an engine body1 having a plurality of cylinders 2, which is driven by being suppliedwith fuel of which a main component is diesel fuel, an intake passage 30through which intake air introduced into the engine body 1 circulates,an exhaust passage 40 through which exhaust gas discharged from theengine body 1 circulates, an exhaust gas recirculation (EGR) device 44which recirculates a portion of the exhaust gas which circulates theexhaust passage 40 to the intake passage 30, and a turbocharger 46 whichis driven by the exhaust gas which passes through the exhaust passage40.

In the engine body 1, the plurality of cylinders 2 are lined up in adirection perpendicular to the drawing sheet of FIG. 1 (in FIG. 1, onlyone of them is illustrated). The engine body 1 includes a cylinder block3, a cylinder head 4, and a piston 5. The cylinder block 3 has cylinderliners which form the cylinders 2. The cylinder head 4 is attached to anupper surface of the cylinder block 3, and covers openings formed at thetop of the cylinders 2. Each piston 5 is reciprocatably accommodatedinside the cylinder 2, and is connected with a crankshaft 7 through aconnecting rod 8. According to the reciprocating motion of the pistons5, the crankshaft 7 rotates on its center axis. The structure of thepiston 5 will be described in full detail later.

Each combustion chamber 6 is formed above the piston 5. The combustionchamber 6 is formed by a lower surface of the cylinder head 4 (a ceilingsurface 6U of the combustion chamber, refer to FIG. 3), the cylinder 2,and a crown surface 50 of the piston 5. The fuel is supplied to thecombustion chamber 6 by an injection from an injector 15 describedlater. A mixture gas of the supplied fuel and air is combusted insidethe combustion chamber 6, and the piston 5 depressed by an expansiveforce of the combustion reciprocates in the vertical direction.

A crank angle sensor SN1 and a water temperature sensor SN2 are attachedto the cylinder block 3. The crank angle sensor SN1 detects a rotationangle of the crankshaft 7 (crank angle), and a rotating speed of thecrankshaft 7 (engine speed). The water temperature sensor SN2 detects atemperature of cooling water or coolant (engine water temperature) whichcirculates inside the cylinder block 3 and the cylinder head 4.

An intake port 9 and an exhaust port 10 which communicate with eachcombustion chamber 6 are formed in the cylinder head 4. In the lowersurface of the cylinder head 4, an intake-side opening which is adownstream end of each intake port 9, and an exhaust-side opening whichis an upstream end of each exhaust port 10 are formed. An intake valve11 which opens and closes each intake-side opening, and an exhaust valve12 which opens and closes each exhaust-side opening are attached to thecylinder head 4. Note that although illustration is omitted, a valvetype of the engine body 1 is the four-valve type comprised of two intakevalves and two exhaust valves, where two intake ports 9 and two exhaustports 10 are provided to each cylinder 2, and two intake valves 11 andtwo exhaust valves 12 are provided to each cylinder 2 as well.

An intake-side valve operating mechanism 13 and an exhaust-side valveoperating mechanism 14 which include a cam shaft respectively, aredisposed in the cylinder head 4. The intake valve 11 and the exhaustvalve 12 are opened and closed by the valve operating mechanisms 13 and14 in an interlocking manner with the rotation of the crankshaft 7. Anintake VVT which can change at least an open timing of the intake valve11 is built in the intake-side valve operating mechanism 13, and anexhaust VVT which can change at least a close timing of the exhaustvalve 12 is built in the exhaust-side valve operating mechanism 14.

In the cylinder head 4, one injector 15 (fuel injection valve) whichinjects fuel into the combustion chamber 6 from a tip-end part thereofis attached to each cylinder 2. The injector 15 injects fuel suppliedthrough a fuel feed pipe (not illustrated) to the combustion chamber 6.The injector 15 is attached to the cylinder head 4 so that the tip-endpart from which the fuel is injected (a nozzle 151 in FIG. 10) islocated at or near the center in the radial direction of the combustionchamber 6, and injects the fuel toward a cavity 5C (FIGS. 2A to 4), aswill be described later, formed in the crown surface 50 of the piston 5.In this embodiment, in order to perform a middle injection within anarrow crank angle range between a pre-injection and a main injectionwhich are described later, it is desirable to use the injector 15 of ahigh-speed response type of which a valve opening response speed (a timerequired for a completion of the valve opening from a start of supply ofelectrical current) is about 50 microseconds to about 200 microseconds.

The injector 15 is connected with a common rail for accumulatingpressure (not illustrated) which is common to all the cylinders 2through the fuel feed pipe. In the common rail, high-pressure fuelpressurized by a fuel feed pump (outside the drawing) is stored. Bysupplying the pressurized fuel inside the common rail to the injector 15of each cylinder 2, the fuel is injected into the combustion chamber 6at high pressure (about 50 MPa to about 250 MPa) from each injector 15.Between the fuel feed pump and the common rail, a fuel pressureregulator 16 (refer to FIG. 5, because not illustrated in FIG. 1) forchanging a fuel injection pressure which is a pressure of the fuelinjected from the injector 15 is provided.

The intake passage 30 is connected to one side surface of the cylinderhead 4 so as to communicate with the intake port 9. Air (fresh air)taken in from an upstream end of the intake passage 30 is introducedinto the combustion chamber 6 through the intake passage 30 and theintake port 9. An air cleaner 31, the turbocharger 46, a throttle valve32, an intercooler 33, and a surge tank 34 are disposed in the intakepassage 30 in this order from the upstream side.

The air cleaner 31 removes foreign substances in intake air to purifythe intake air. The throttle valve 32 interlocks with a stepping-onoperation of an accelerator pedal (not illustrated) to open and closethe intake passage 30, thereby adjusting a flow rate of the intake airin the intake passage 30. The turbocharger 46 sends out the intake airto the downstream side of the intake passage 30, while compressing theintake air. The intercooler 33 cools the intake air compressed by thesupercharger 46. The surge tank 34 is a tank which is disposed at animmediately upstream location of an intake manifold which continues tothe intake port 9, and provides space for equally distributing theintake air to the plurality of cylinders 2.

An airflow sensor SN3, an intake air temperature sensor SN4, an intakepressure sensor SN5, and an intake O₂ sensor SN6 are disposed in theintake passage 30. The airflow sensor SN3 is disposed at the downstreamside of the air cleaner 31, and detects a flow rate of the intake airwhich passes through this portion. The intake air temperature sensor SN4is disposed at the downstream side of the intercooler 33, and detects atemperature of the intake air which passes through this portion. Theintake pressure sensor SN5 and the intake O₂ sensor SN6 are disposednear the surge tank 34, and detect a pressure and an oxygenconcentration of the intake air which passes through this portion,respectively. Note that although not illustrated in FIG. 1, an injectionpressure sensor SN7 (FIG. 5) which detects an injection pressure of fuelfrom the injector 15 is provided.

The exhaust passage 40 is connected to the other side surface of thecylinder head 4 so as to communicate with the exhaust port 10. Burnt gas(exhaust gas) generated inside the combustion chamber 6 is discharged tothe exterior of the vehicle through the exhaust port 10 and the exhaustpassage 40. An exhaust emission control device 41 is provided in theexhaust passage 40. An oxidation catalyst 42 which oxidizes anddetoxicates hazardous constituents (CO and HC) contained in exhaust gas,and a DPF (Diesel Particulate Filter) 43 for capturing particulatematters contained in the exhaust gas are built in the exhaust emissioncontrol device 41. Note that a NO_(x) catalyst which reduces anddetoxicates NO_(x) may further be disposed at a position on thedownstream side of the exhaust emission control device 41 in the exhaustpassage 40.

An exhaust O₂ sensor SN8 and a pressure difference sensor SN9 aredisposed in the exhaust passage 40. The exhaust O₂ sensor SN8 isdisposed between the turbocharger 46 and the exhaust emission controldevice 41, and detects an oxygen concentration of exhaust gas whichpasses through this portion. The pressure difference sensor SN9 detectsa pressure difference between an upstream end and a downstream end ofthe DPF 43.

The EGR device 44 includes an EGR passage 44A which connects the exhaustpassage 40 with the intake passage 30, and an EGR valve 45 provided tothe EGR passage 44A. The EGR passage 44A connects a portion of theexhaust passage 40 at the upstream side of the turbocharger 46 with aportion of the intake passage 30 between the intercooler 33 and thesurge tank 34. Note that an EGR cooler (not illustrated) which coolsexhaust gas (EGR gas) recirculating from the exhaust passage 40 to theintake passage 30 by a heat exchange is disposed in the EGR passage 44A.The EGR valve 45 adjusts a flow rate of exhaust gas which circulates theEGR passage 44A.

The turbocharger 46 includes a compressor 47 disposed at the intakepassage 30 side, and a turbine 48 disposed at the exhaust passage 40side. The compressor 47 and the turbine 48 are coupled to each otherthrough a turbine shaft so that they are integrally rotatable. Theturbine 48 is rotated by receiving energy of the exhaust gas that flowsthrough the exhaust passage 40. By the compressor 47 being rotated inthe interlocked manner, air which circulates the intake passage 30 iscompressed (supercharged or boosted).

[Detailed Structure of Piston]

Next, the structure of the piston 5, particularly, the structure of thecrown surface 50 is described in detail. FIG. 2A is a perspective viewmainly illustrating an upper part of the piston 5. Although the piston 5includes a piston head located on the upper side and a skirt partlocated on the lower side, FIG. 2A illustrates the piston head parthaving the crown surface 50 in a top surface thereof. FIG. 2B is aperspective view illustrating a radial cross-section of the piston 5.FIG. 3 is an enlarged view of the radial cross-section illustrated inFIG. 2B. Note that in FIGS. 2A and 2B, a cylinder axis direction A and aradial direction B of the combustion chamber are illustrated by arrows.

The piston 5 includes the cavity 5C, a peripheral flat surface part 55,and a side circumferential surface 56. A part of a wall surface of thecombustion chamber surface (the bottom surface) which defines thecombustion chamber 6 is formed by the crown surface 50 of the piston 5,and the cavity 5C is provided to the crown surface 50. The cavity 5C isa portion of the crown surface 50 which is recessed downwardly in thecylinder axis direction A, and is a portion which receives the injectionof fuel from the injector 15. The peripheral flat surface part 55 is anannular flat surface part disposed in an area of the crown surface 50near a perimeter edge in the radial direction B. The cavity 5C isdisposed in a center area of the crown surface 50 in the radialdirection B, excluding the peripheral flat surface part 55. The sidecircumferential surface 56 is a surface which slidably contacts an innerwall surface of the cylinder 2, and is provided with a plurality of ringgrooves into which piston rings (not illustrated) are fitted.

The cavity 5C includes a first cavity part 51, a second cavity part 52,a connecting part 53, and a mountain part 54. The first cavity part 51is a recessed part disposed in the center area of the crown surface 50in the radial direction B. The second cavity part 52 is an annularrecessed part disposed at the perimeter side of the first cavity part 51in the crown surface 50. The connecting part 53 is a part which connectsthe first cavity part 51 with the second cavity part 52 in the radialdirection B. The mountain part 54 is a mountain-shaped convex partdisposed in the center position of the crown surface 50 (the firstcavity part 51) in the radial direction B. The mountain part 54 isbulged at a position directly under the nozzle 151 of the injector 15(FIG. 10).

The first cavity part 51 includes a first upper end part 511, a firstbottom part 512, and a first inner end part 513. The first upper endpart 511 is located at the highest position of the first cavity part 51,and continues to the connecting part 53. The first bottom part 512 is anannular area in a plan view which is recessed most in the first cavitypart 51. As for the entire cavity 5C, this first bottom part 512 is thedeepest part, and the first cavity part 51 has a given depth (a firstdepth) in the cylinder axis direction A in the first bottom part 512. Inthe plan view, the first bottom part 512 is located at a position closeto and inward of the connecting part 53 in the radial direction B.

Between the first upper end part 511 and the first bottom part 512, theyare connected by a radially dented part 514 which curves outwardly inthe radial direction B. The radially dented part 514 has a portion whichis dented outwardly in the radial direction B from the connecting part53. The first inner end part 513 is located at the most radially inwardposition in the first cavity part 51, and continues to a lower end ofthe mountain part 54. Between the first inner end part 513 and the firstbottom part 512, they are connected by a curved surface which curvesgently in the shape of foot of a mountain.

The second cavity part 52 includes a second inner end part 521, a secondbottom part 522, a second upper end part 523, a taper area 524, and astanding wall area 525. The second inner end part 521 is located at themost radially inward position of the second cavity part 52, andcontinues to the connecting part 53. The second bottom part 522 is amost dented area in the second cavity part 52. The second cavity part 52has a depth (a second depth) in the cylinder axis direction A, shallowerthan the first bottom part 512 in the second bottom part 522. That is,the second cavity part 52 is a recessed part located above in thecylinder axis direction A from the first cavity part 51. The secondupper end part 523 is the highest position in the second cavity part 52,is located at the most radially outside, and continues to the peripheralflat surface part 55.

The taper area 524 extends toward the second bottom part 522 from thesecond inner end part 521, and is a portion having such a surface shapethat it inclines downwardly in the radially outward direction. Asillustrated in FIG. 3, the taper area 524 has an inclination along aninclination line C2 which intersects with a horizontal line C1 extendingin the radial direction B, by an inclination angle α.

The standing wall area 525 is a wall surface formed so as to risecomparatively steeply from a location radially outward of the secondbottom part 522. In the cross-sectional shape in the radial direction B,the portion from the second bottom part 522 to the second upper end part523, which is a curved surface which curves so that the wall surface ofthe second cavity part 52 goes up from the horizontal direction, and isa wall surface which is almost a vertical wall near the second upper endpart 523, is the standing wall area 525. A lower part of the standingwall area 525 is located inwardly in the radial direction B from anupper end position of the standing wall area 525. Thus, combustion inwhich the mixture gas is prevented from excessively returning inwardlyin the radial direction B of the combustion chamber 6, and a space (asquish space) radially outward of the standing wall area 525 iseffectively utilized can be performed.

The connecting part 53 has a shape in the cross-sectional shape in theradial direction B, between the first cavity part 51 located at thelower side and the second cavity part 52 located at the upper side,which projects in a bump shape radially inwardly. The connecting part 53has a lower end part 531, a third upper end part 532 (an upper end partin the cylinder axis direction), and a center part 533 located at thecenter therebetween. The lower end part 531 is a connecting part to thefirst upper end part 511 of the first cavity part 51. The third upperend part 532 is a connecting part to the second inner end part 521 ofthe second cavity part 52.

In the cylinder axis direction A, the lower end part 531 is a portionlocated at the lowest position of the connecting part 53, and the thirdupper end part 532 is a portion located at the highest position. Thetaper area 524 described above is also an area which extends toward thesecond bottom part 522 from the third upper end part 532. The secondbottom part 522 is located below the third upper end part 532. That is,the second cavity part 52 of this embodiment does not have a bottomsurface which extends horizontally and outwardly in the radial directionB from the third upper end part 532, and, in other words, the portionsfrom the third upper end part 532 to the peripheral flat surface part 55are not connected through a horizontal surface, but have the secondbottom part 522 depressed downwardly from the third upper end part 532.

Although the mountain part 54 projects upwardly, the projection heightis the same as the height of the third upper end part 532 of theconnecting part 53, and the top of the projection is located at a moredented location from the peripheral flat surface part 55. The mountainpart 54 is located at the center of the first cavity part 51 which iscircular in the plan view, and, thereby, the first cavity part 51 is anannular groove formed around the mountain part 54.

[Curved Surface Shape of Cavity Part]

FIG. 4 is a cross-sectional view in the cylinder axis direction A,illustrating the curved surface shape of the first and second cavityparts 51 and 52 and the connecting part 53. The first cavity part 51 isprovided, in the cross-section including the cylinder axis, with asurface shape which follows a Descartes' egg-shaped oval curve(hereinafter, referred to as the “Egg Shape”). In detail, the firstcavity part 51 includes a first portion R1 of an arc shape locatedfurthest from the injector 15 (an injection hole 152), a second portionR2 located between the first portion R1 and the connecting part 53, anda third portion R3 extending inwardly in the radial direction B from thefirst portion R1. If the shape is applied to the shape in FIG. 3, thefirst portion R1 corresponds to a center area of the radially dentedpart 514, the second portion R2 corresponds to an area extending fromthe radially dented part 514 to the first upper end part 511, and thethird portion R3 corresponds to an area extending from the radiallydented part 514 to the first bottom part 512.

FIG. 4 illustrates a state where an injection axis AX of fuel injectedfrom the injector 15 intersects with the first portion R1 furthest fromthe injector 15. The Egg Shape of the first cavity part 51 is an arcshape in which a radius r1 of such a first portion R1 is the smallest,and the radius increases continuously as it goes toward the secondportion R2 from the first portion R1, and as it goes toward the thirdportion R3 from the first portion R1. That is, a radius r2 of the secondportion R2 increases as it separates from the first portion R1 in thecounterclockwise direction in the cross-section of FIG. 4. Moreover, theradius r3 of the third portion R3 increases at the same rate as theradius r2 of the second portion R2 (r2=r3) as it separates from thefirst portion R1 in the clockwise direction. If the Egg Shape isexpressed by using the connecting part 53 as a starting point, it has anarc shape in which the radius of the arc decreases from the secondportion R2 to the first portion R1, and the radius of the arc increasesfrom the first portion R1 to the third portion R3.

The connecting part 53 has a convex surface shape comprised of a curvedsurface having a given radius r4 from the lower end part 531 (the firstupper end part 511) to the third upper end part 532 (the second innerend part 521). The second cavity part 52 has a concave surface shapecomprised of a curved surface having a given radius r5, from the secondbottom part 522 to the standing wall area 525. The second upper end part523 has a convex surface shape comprised of a curved surface having agiven radius r6. Suppose that a distance in the cylinder axis directionA between the center point of the radius r4 and the center point of theradius r5 is a second distance Sv, and a distance in the radialdirection B between the center point of the radius r5 and the centerpoint of the radius r6 is a first distance Sh, numerical values of theradii r4, r5, and r6 are selected so that the following relationshipsare satisfied.

r4+r5>Sv

r5+r6≤Sh

In the second cavity part 52, a portion extending from the second bottompart 522 to an upper end position R4 of the standing wall area 525 isformed by an approximately quarter circular shape (¼ circle) of theradius r5. The upper end position R4 of the standing wall area 525continues to a lower end position of the second upper end 523 comprisedof an approximately quarter circular shape of the radius r6. Note thatan upper end of the second upper end part 523 continues to theperipheral flat surface part 55. As a result of being formed in such acurved surface shape, the lower part of the standing wall area 525 islocated inward in the radial direction B of the upper end position R4 ofthe standing wall area 525. That is, the standing wall area 525 does nothave a portion scooped out outwardly in the radial direction B, unlikethe radially dented part 514 of the first cavity part 51. Althoughdescribed in full detail later, the reason why the standing wall area525 is formed in such an arc shape is that the mixture gas is preventedfrom excessively returning inwardly in the radial direction B of thecombustion chamber 6, by collaborating with the Egg Shape of the firstcavity part 51, and the combustion in which the space (squish space)outward in the radial direction B of the standing wall area 525 iseffectively utilized is performed.

[Control Configuration]

Next, a control configuration of the diesel engine system is describedbased on a block diagram of FIG. 5. The diesel engine system of thisembodiment is integrally controlled by a controller 70 (engine controldevice). The controller 70 is comprised of a processor 79 (e.g., acentral processing unit (CPU)) having associated ROM, RAM, etc.Detection signals from various sensors mounted to the vehicle areinputted into the controller 70. In addition to the sensors SN1-SN9described above, the vehicle is provided with an accelerator openingsensor SN10 which detects an accelerator opening, an atmosphericpressure sensor SN11 which measures the atmospheric pressure of theoperating environment around the vehicle, and an ambient temperaturesensor SN12 which measures a temperature of the operating environmentaround the vehicle.

The controller 70 is electrically connected to the crank angle sensorSN1, the water temperature sensor SN2, the airflow sensor SN3, theintake air temperature sensor SN4, the intake pressure sensor SN5, theintake O₂ sensor SN6, the injection pressure sensor SN7, the exhaust O₂sensor SN8, the pressure difference sensor SN9, the accelerator openingsensor SN10, the atmospheric pressure sensor SN11, and the ambienttemperature sensor SN12, which are described above. Information detectedby these sensors SN1-SN12, that is, information including the crankangle, the engine speed, the engine water temperature, the intake airflow rate, the intake air temperature, the intake pressure, the intakeoxygen concentration, the fuel injection pressure of the injector 15,the exhaust oxygen concentration, the accelerator opening, the ambienttemperature, and the atmospheric pressure are sequentially inputted intothe controller 70.

The controller 70 controls each part of the engine, while performingvarious determinations, calculations, etc. based on the input signalsfrom the sensors SN1-SN12, etc. That is, the controller 70 iselectrically connected with the injectors 15 (fuel pressure regulator16), the throttle valve 32, and the EGR valve 45, and outputs controlsignals to these apparatuses based on results of the calculations,respectively.

The controller 70 executes software modules to achieve their respectivefunctions, including a target torque setting module 71 and a fuelinjection controlling module 72, which controls operation of theinjector 15. These modules are stored in memory 78 as software.

The target torque setting module 71 sets a target torque of the engineaccording to an operating condition. In detail, the target torquesetting module 71 sets the target torque of the engine based on theaccelerator opening detected by the accelerator opening sensor SN10.

The fuel injection controlling module 72 controls a fuel injectionoperation by the injector 15. In each cycle of an operating range wherepremixed compression ignition combustion is applied (PCI range), thefuel injection controlling module 72 causes the injector 15 to performat least three injections including the pre-injection (first injection),the main injection (second injection) performed at the retarding side ofthe pre-injection, and the middle injection performed at a timingbetween the pre-injection and the main injection. That is, a fuelinjection amount to be supplied to the combustion chamber 6 during onecycle is secured by the pre-injection, the main injection, and themiddle injection.

The fuel injection controlling module 72 operates so as to functionallybe provided with an operating condition determining module 73, aninjection amount setting module 74, an injection pattern setting module75, an estimating module 76, and a correcting module 77.

The operating condition determining module 73 acquires operatingcondition information, such as an engine speed, an engine load, anengine water temperature, an engine oil temperature, an ambienttemperature, an intake air temperature, an intake pressure, an oxygenconcentration, and a valve opening of the EGR valve 45 based ondetection values of the sensors SN1-SN12, and determines the operatingcondition, etc. of the engine body 1.

The injection amount setting module 74 sets an injection amount of fuelto be injected from the injector 15 per one cycle. The injection amountto be set is a target injection amount which achieves the target torquewhich is set by the target torque setting module 71.

The injection pattern setting module 75 reads a setting map of theinjection pattern which is preset for every target injection amount (acombination of the engine speed and the engine load), and sets theinjection pattern according to the target injection amount. Theinjection pattern setting becomes a pattern including the pre-injection,the main injection, and the middle injection, when the operatingcondition determining module 73 determines the operating condition is atleast the PCI range. Moreover, as for the pre-injection and the maininjection, injection timings and an injection amount ratio of both theinjections are set so that pressure waves respectively resulting fromthe combustions caused by these injections cancel each other out.Further, a fuel injection amount of the middle injection is less thanthe fuel injection amounts of the pre-injection and the main injection,and is set so that a part of the injection amount respectively assignedto the pre-injection and the main injection is decreased whilemaintaining the injection amount ratio, and the decreased amount isassigned the middle injection. Note that the injection pattern settingmodule 75 may sequentially set the injection pattern based on theoperating condition information acquired by the operating conditiondetermining module 73 and the target injection amount, without dependingon the setting map.

The estimating module 76 estimates an occurring timing of a peak of theheat release rate of the premix combustion by the pre-injection, withreference to a fuel injection timing of the pre-injection set by theinjection pattern setting module 75, and a given combustionenvironmental factor which affects the combustion inside the combustionchamber 6. The estimating module 76 uses a given estimation modelequation for this estimation (this will be described later withreference to FIG. 15). When the peak of the heat release rate of thepremix combustion is offset due to the combustion environmental factor,since it becomes impossible to achieve a target heat release ratecharacteristic (achieved by the injection pattern as scheduled by thesetting map) set so that the pressure waves could cancel each other out,the estimating module 76 performs a calculation to obtain the offset.The peak of the heat release rate of the premix combustion can beadjusted by a feedback control based on the detection results of thevarious sensors SN1-SN12. However, in the feedback control, a dieselknocking noise may occur in actual case, which may make a driveruncomfortable. Therefore, the estimating module 76 estimates the offsetby a feed-forward approach which uses the estimation model equation.

The correcting module 77 corrects the fuel injection timing of thepre-injection set by the injection pattern setting module 75, based onthe occurring timing of the peak of the heat release rate of the premixcombustion estimated by the estimating module 76. That is, thecorrecting module 77 corrects the fuel injection timing so that theoffset between the occurring timing of the peak of the heat release ratewhen performing the pre-injection at the fuel injection timing accordingto the setting map and the occurring timing of the peak of the heatrelease rate estimated by the estimating module 76 with reference to thecombustion environmental factor is canceled out. That is, the correctionto cancel the offset is performed before the diesel knocking noiseoccurs.

The memory 78 stores the setting map which is referred when theinjection pattern setting module 75 sets the injection pattern.Moreover, the memory 78 stores the estimation model equation used whenthe estimating module 76 performs the given calculation. In addition,the memory 78 stores various kinds of programs and various kinds ofsettings.

[Example of Injection Pattern]

Next, one example of the injection pattern of fuel set by the injectionpattern setting module 75, and the heat release rate characteristicresulting from the combustion caused by the injection are described.FIG. 6 is a time chart illustrating a timing of the fuel injection, anda heat release rate characteristic H. As described above, the fuelinjection controlling module 72 causes the injector 15 to perform apre-injection P1, a main injection P2, and a middle injection P3.

The pre-injection P1 is performed at a timing when the piston 5 islocated at the advancing side of a compression top dead center (TDC).The pre-injection P1 aims at that the premix combustion of the injectedfuel is carried out, and is performed in a later stage of thecompression stroke where an in-cylinder pressure and an in-cylindertemperature become high to some extent. In FIG. 6, the example where thepre-injection P1 is performed during a period of one crank angle (−CA16deg) to another crank angle (−CA12 deg) is illustrated. As for a spatialrelationship with the cavity 5C, the pre-injection P1 is set at a timing(crank angle) where the injector 15 can inject fuel toward theconnecting part 53. That is, the pre-injection P1 is performed at atiming where the injection axis AX of the injector 15 intersects withthe connecting part 53.

The main injection P2 is located at the retarding side of thepre-injection P1, and is started during a period of the fuel injected bythe pre-injection P1 being carrying out the premix combustion. That is,the main injection P2 aims at that diffuse combustion of the fuelinjected using the heat of the premix combustion is carried out, and isa fuel injection which is started at a timing where the piston 5 islocated substantially near a TDC. In FIG. 6, the example where the maininjection P2 is performed at a timing where the piston 5 is located at aslightly retarding side of the TDC is illustrated. As for the spatialrelationship with the cavity 5C, the main injection P2 is set as thetiming where the injector 15 can inject fuel toward the first cavitypart 51. Although the peak value of the fuel injection rate is the samefor the pre-injection P1 and the main injection P2, a fuel injectionperiod (that is, the fuel injection amount) of the pre-injection P1 isset longer (more).

The middle injection P3 is an injection performed at the timing betweenthe pre-injection P1 and the main injection P2. The fuel injected by themiddle injection P3 is to combust between the combustion of thepre-injection P1 and the combustion of the main injection P2. The middleinjection P3 is also diffuse combustion in general. FIG. 6 illustratesthe example where the middle injection P3 is started from a crank angleof −CA6 deg. The fuel injection period (fuel injection amount) of themiddle injection P3 is set shorter (less) than both of the pre-injectionP1 and the main injection P2.

The heat release rate characteristic H by the respective combustion ofthe pre-injection P1, the main injection P2, and the middle injection P3is illustrated in FIG. 6. The heat release rate characteristic H is acharacteristic deeply related with an increasing rate of the combustionpressure inside the combustion chamber 6, and has an earlier-stagecombustion portion HA which is a mountain part caused by the premixcombustion accompanying the pre-injection P1, a later-stage combustionportion HB which is caused by the diffuse combustion accompanying themain injection P2, and a middle combustion portion HC which is in themiddle of both the combustion portions HA and HB. That is, in the heatrelease rate characteristic H, the peak of the heat release rate appearsin two steps, resulting from the respective combustions of thepre-injection P1 and the main injection P2 with comparatively largerinjection amounts which are performed at separated timings. Althoughdescribed in full detail later, the middle injection P3 is an injectionfor lowering the peaks of the heat release rate resulting from therespective combustions of the pre-injection P1 and the main injectionP2.

[Two-Step Peak of Heat Release Rate and Cancelation of Combustion Noise]

The pre-injection P1 and the main injection P2 are performed so that thepressure waves resulting from the respective combustions caused by theseinjections cancel each other out. That is, the fuel injectioncontrolling module 72 causes the injector 15 to perform thepre-injection P1 and the main injection P2 so that the respectivecombustions occur at the timings where combustion noises resulting fromthe respective injections can cancel each other out. This is describedwith reference to FIG. 7.

FIG. 7A illustrates a heat release rate characteristic HO having thetwo-step peak of the heat release rate, similar to the heat release ratecharacteristic H illustrated in FIG. 6. The heat release ratecharacteristic HO illustrated here is a characteristic when notperforming the middle injection P3, and, therefore, a value of anearlier-stage peak HAp of the earlier-stage combustion portion HA and avalue of a later-stage peak HBp of the later-stage combustion portion HBbecome larger accordingly. In other words, a degree of fall of the heatrelease rate in the middle combustion portion HC increases.

An interval “In” (peak interval) between a timing when the earlier-stagepeak HAp occurs and a time when the later-stage peak HBp occurs largelyinfluences the reduction of combustion noise. If the interval isappropriately set so that an amplitude of a pressure wave (sound wave)resulting from the combustion of the earlier-stage combustion portion HAand an amplitude of a pressure wave resulting from the combustion of thelater-stage combustion portion HB cancel each other out, the appearingpressure wave (combustion noise) can then be reduced by the frequencyeffect.

FIG. 7B is a schematic diagram illustrating the cancelation effect ofthe pressure waves. In FIG. 7B, an earlier-stage pressure wave EAwresulting from the combustion of the earlier-stage combustion portionHA, and a later-stage pressure wave EBw resulting from the combustion ofthe later-stage combustion portion HB are illustrated. Here, in order tosimplify the description, it is assumed that a peak height of theearlier-stage peak HAp and a peak height of the later-stage peak HBp arethe same, and the amplitude of the earlier-stage pressure wave EAw andthe amplitude of the later-stage pressure wave EBw are the same. Here,in order to cancel out both the pressure waves, the earlier-stagepressure wave EAw and the later-stage pressure wave EBw may appear witha ½ cycle offset. That is, a pressure-wave interval “Fin” until theoccurrence of the later-stage pressure wave EBw following theearlier-stage pressure wave EAw may be set in a half (½) of the cycle ofeach of the pressure waves EAw and EBw. In this case, the earlier-stagepressure wave EAw and the later-stage pressure wave EBw may becomeopposite phases to each other and interfere with each other so that theycancel each other out, and, therefore, the amplitude of their syntheticwave EM becomes zero. That is, combustion noise is canceled out by thecancelation effect. Therefore, if the fuel injection controlling module72 performs the pre-injection P1 and the main injection P2 so that thelater-stage pressure wave EBw occurs ½ cycle behind of the earlier-stagepressure wave EAw, combustion noise can theoretically be reduced.

However, as described above, a combustion mode differs between thecombustion by the pre-injection P1 (premix combustion) and thecombustion by the main injection P2 (diffuse combustion). Therefore, thestandup characteristics, etc. of the heat release rates by both thecombustions become different from each other, and, as a result, afrequency component of the earlier-stage pressure wave EAw and afrequency component of the later-stage pressure wave EBw becomenaturally different. Even if the representative frequency components ofboth the pressure waves EAw and EBw are adjusted to be opposite phases,other frequency components do not become opposite phases, and therefore,both the pressure waves EAw and EBw cannot fully cancel each other out.Therefore, the present inventors recognized that, even if thepre-injection P1 and the main injection P2 which aim at the ½ cycleoffset of both the pressure waves EAw and EBw were actually performed,combustion noise could not fully be reduced.

In this embodiment, the above problem is solved by directly reducing theearlier-stage and later-stage peaks HAp and HBp of the earlier-stage andlater-stage combustion portions HA and HB in the heat release ratecharacteristic H, while aiming at the ½ cycle offset of both thepressure waves EAw and EBw. The middle injection P3 is performed inorder to reduce the earlier-stage and later-stage peaks HAp and HBp.That is, the fuel injection amount required for one cycle is secured bythe execution of the middle injection P3 in addition to thepre-injection P1 and the main injection P2. Therefore, the injectionamounts of the pre-injection P1 and the main injection P2 can be reducedby the injection amount of the middle injection P3, and the peaks of theheat release rates by the respective combustions of the pre-injection P1and the main injection P2 can be reduced accordingly.

In FIG. 8, the heat release rate characteristic HO (a solid line) whenonly the pre-injection P1 and the main injection P2 are performed, and aheat release rate characteristic Hx (a broken line; corresponding to theheat release rate characteristic H of FIG. 6) when the middle injectionP3 is performed in addition to the pre-injection P1 and the maininjection P2 are illustrated. The fuel injection controlling module 72decreases a part of the injection amount assigned to the pre-injectionP1 and the main injection P2, while maintaining the injection amountratio of the pre-injection P1 and the main injection P2, and performsthe middle injection P3 while assigning the reduced injection amount tothe middle injection P3. Therefore, as illustrated in FIG. 8, theearlier-stage peak HAp of the earlier-stage combustion portion HA fallsaccording to the reduced amount of the pre-injection P1, and thelater-stage peak HBp of the later-stage combustion portion HB also fallsaccording to the reduced amount of the main injection P2. Thus, sincethe peaks HAp and HBp of the heat release rate can be reduced, themagnitudes of the pressure waves EAw and EBw resulting from therespective combustions of the pre-injection P1 and the main injection P2can be reduced. Combustion noise also decreases because the amplitudesof the pressure wave EAw and EBw become smaller. Therefore, combustionnoise can effectively be reduced with the combination with the injectionmode to cancel out the pressure waves EAw and EBw.

On the other hand, the heat release rate of the middle combustionportion HC is increased. Since the middle injection P3 is performed atthe timing between the pre-injection P1 and the main injection P2, thecombustion by the middle injection P3 serves to fill the valley betweenthe earlier-stage peak HAp and the later-stage peak HBp. Therefore, theheat release rate of the middle combustion portion HC is raised. Thus,unlike the post injection performed at the retarding side of the maininjection P2, the combustion by the middle injection P3 directlycontributes to the engine torque, and will not reduce thermalefficiency. In addition, since the middle injection P3 is performed withthe injection amount less than the pre-injection P1 and the maininjection P2, it becomes possible to complete the combustion before themain injection P2, without affecting the combustion by the maininjection P2. That is, since the combustion mode of the main injectionP2 set so that the pressure waves EAw and EBw cancel each other out canbe maintained, the cancelation effect of combustion noises will not bereduced.

[Desirable Fuel Injection Mode]

FIG. 9 is a schematic diagram illustrating a relationship between starttimings and end timings of the pre-injection P1, the main injection P2,and the middle injection P3, and penetrations d1, d2, and d3 of theinjections P1, P2, and P3 (injection distance). Below, the desirableinjection modes of the respective injections P1-P3 are described withreference to FIG. 9.

<Pre-Injection>

First, the fuel injection controlling module 72 is desirable to causethe injector 15 to perform the pre-injection P1 at the final stage of acompression stroke. In detail, when the compression stroke is equallydivided into four by the crank angle, it is desirable to perform thepre-injection P1 in the final quarter period. The pre-injection P1 is aninjection for the premix combustion performed at the advancing side of aTDC, as described above. In order to realize appropriate premixcombustion, it is desirable to carry out the fuel injection at the finalstage of the compression stroke.

That is, if the crank angle reaches the final quarter period of thecompression stroke, although the in-cylinder temperature of thecombustion chamber 6 does not reach the ignition temperature, thein-cylinder temperature is raised to some extent, and, therefore, acondition advantageous to the combustion of the mixture gas isestablished. When a part or all of the pre-injection P1 is performed atthe first half of a compression stroke, or an intake stroke, there isconcern that fuel spray injected from the injector 15 adheres to aninner wall surface of the cylinder 2 to induce soot and deposit. On theother hand, since premixed mixture gas is exposed to the environmentwhere the fuel very easily combusts in the final quarter period of thecompression stroke, the fuel can be combusted without reaching the innerwall surface of the cylinder 2. Of course, if the pre-injection P1 isperformed at a too-late timing, the premix combustion cannot berealized, and the interval In during which the pressure-wavecancellation with the main injection P2 is performed cannot be secured.Therefore, it is desirable to perform the pre-injection P1 in the finalquarter period of the compression stroke, while satisfying the conditionwhich can achieve the premix combustion and the pressure-wavecancellation.

<Penetration of Each Injection>

Next, the desirable penetrations (injection distances) d1-d3 of therespective injections P1-P3 are described. When performing thepre-injection P1 and the main injection P2, the fuel injectioncontrolling module 72 is desirable to set the injection period of theinjector 15 so that the fuel spray injected from the injector 15 becomesa penetration which reaches the wall surface defining the combustionchamber 6 (the inner wall surface of the cavity 5C and the inner wallsurface of the cylinder 2). On the other hand, when performing themiddle injection P3, the fuel injection controlling module 72 isdesirable to set the injection period of the injector 15 so that thefuel spray becomes a penetration which does not reach the wall surfaceof the combustion chamber 6.

In FIG. 9, the inner wall surface of the cavity 5C is assumed to be thewall surface. In the pre-injection P1, a start timing CA1 and an endtiming CA2 of the pre-injection P1 (injection period) are set so thatthe penetration d1 which reaches the inner wall surface of the cavity 5Cis obtained. In the pre-injection P1, the inner wall surface of thecavity 5C is a wall surface of the connecting part 53. Similarly, alsoin the main injection P2, a start timing CA5 and an end timing CA6 ofthe main injection P2 are set so that the penetration d2 which reachesthe inner wall surface of the cavity 5C is obtained. In the maininjection P2, the inner wall surface of the cavity 5C is a wall surfaceof the first cavity part 51.

On the other hand, in the middle injection P3, a start timing CA3 and anend timing CA4 of the middle injection P3 are set so that thepenetration d3 which does not reach the inner wall surface of the cavity5C is obtained. In detail, the penetration d3 that is shorter than adistance from the injection hole 152 of the injector 15 to the innerwall surface of the cavity 5C at the injection timing of the middleinjection P3 is set. In other words, the fuel injection period of themiddle injection P3 is set shorter than the pre-injection P1 and themain injection P2 so that such a penetration d3 can be obtained. As aresult, since the fuel injection pressure when the injector 15 is openedis constant and the injection period is proportional to the injectionamount, the fuel injection amount of the middle injection P3 is set toan amount smaller than the pre-injection P1 and the main injection P2.

By setting the penetrations d1-d3 as described above, the combustionwhich effectively uses the space (oxygen) inside the combustion chamber6 can be realized. That is, since the fuel injected by the pre-injectionP1 and the main injection P2 is sprayed with the comparatively largepenetrations d1 and d2, the combustion can be carried out using oxygenexisting in the area radially outward of the combustion chamber 6. Onthe other hand, since the fuel injected by the middle injection P3 issprayed with the comparatively small penetration d3, the combustion canbe carried out using the space in the radially center area of thecombustion chamber 6. Therefore, the fuel injected by the middleinjection P3 can certainly contribute to the engine torque. This issuewill further be described later with reference to FIGS. 10 to 13.

<Start Timing and End Timing of Main Injection>

Desirable start and end timings of the main injection P2 are described.As described above, the main injection P2 is an injection which beginsduring the combustion period by the pre-injection P1 and causes thediffuse combustion utilizing the heat caused by the combustion of thepre-injection P1. In this nature, the main injection P2 is performednear a TDC. Here, the fuel injection controlling module 72 is desirableto set the injection period of the main injection P2 so that the starttiming CA5 of the main injection P2 is closer to TDC compared to the endtiming CA6 of the main injection P2.

When the start timing CA5 of the main injection P2 is set wastefullyearlier, some or all of the fuel injected by the main injection P2 maynot carry out the diffuse combustion. In order to certainly cause thediffuse combustion by the main injection P2, it is desirable to performthe main injection P2 after the peak of the combustion by thepre-injection P1 (the earlier-stage peak HAp illustrated in FIG. 8),i.e. after the in-cylinder temperature and pressure of the combustionchamber 6 become high enough. As described above, if the start timingCA5 is set closer to TDC compared to the end timing CA6, the maininjection P2 will not be performed too early. Therefore, the explosivepower by the diffuse combustion based on the main injection P2 can moreefficiently be converted to engine torque.

<Start Timing of Middle Injection>

The middle injection P3 is an injection of the small penetration d3,performed at the timing between the pre-injection P1 and the maininjection P2. As for such a middle injection P3, the fuel injectioncontrolling module 72 is desirable to set the start timing CA3 of themiddle injection P3 at a timing closer to the start timing CA5 of themain injection P2 than the end timing CA2 of the pre-injection P1.

The fuel injected by the middle injection P3 may be caught in the fuelinjected by the main injection P2, if the combustion is not started bythe start timing CA5 of the main injection P2. That is, before the fuelspray of the middle injection P3 combusts, the fuel spray of the middleinjection P3 may be caught in the fuel spray of the main injection P2and it may be carried to an area radially outward of the combustionchamber 6. In this case, it is assumed that the fuel of the middleinjection P3 and the fuel of the main injection P2 are combusted in thesame area of the combustion chamber 6, and oxygen inside the combustionchamber 6 is not effectively utilized. Moreover, the effects of directlylowering the later-stage peak HBp and reducing combustion noise is alsodiminished.

However, if the timing setup is performed as described above, the middleinjection P3 can be started at the timing close to the start timing CA5of the main injection P2. It may appear that the combustion of themiddle injection P3 is delayed, but the start timing CA3 of the middleinjection P3 is retarded more with respect to the end timing CA2 of thepre-injection P1. That is, the fuel of the middle injection P3 issupplied to the environment inside the combustion chamber 6 where thein-cylinder temperature is fully raised by the premix combustion by thepre-injection P1. Therefore, the fuel injected by the middle injectionP3 can be combusted immediately, and being caught in the injected fuelof the main injection P2 can be prevented.

<Relationship of Injection Amount Between Three Injections>

As for a relationship between the injection amount of the pre-injectionP1 and the main injection P2, the fuel injection controlling module 72is desirable to set the fuel amount injected by the pre-injection P1more than the fuel amount injected by the main injection P2. That is, itis desirable to set a period between the start timing CA1 to the endtiming CA2 of the pre-injection P1 longer than a period between thestart timing CA5 to the end timing CA6 of the main injection P2.

The pre-injection P1 is an injection directed to the connecting part 53of the cavity 5C, and utilizes both the spaces of the first and secondcavity parts 51 and 52. On the other hand, in the main injection P2, thespace of the first cavity part 51 is exclusively utilized. That is, thepre-injection P1 becomes the injection for the larger space. Accordingto such a use of the spaces, oxygen inside the combustion chamber 6 canefficiently be used in each injection by setting the fuel amount in thepre-injection P1 more than the main injection P2. This issue will beillustrated later.

The injection amount ratio of the pre-injection P1, the main injectionP2, and the middle injection P3 is set suitably according to theoperating condition, based on the condition where the middle injectionP3 is performed with the less injection amount than the pre-injection P1and the main injection P2. For example, if the injector 15 is 600 kPa inthe injection pressure, and the engine speed is 2,000 rpm, eachinjection amount can be set as follows.

-   -   Pre-injection P1: 11.1 mm³    -   Main injection P2: 7.8 mm³    -   Middle injection P3: 3.6 mm³        As being apparent from this example setting, the injection        amount of the middle injection P3 is set less than about ⅓ of        the pre-injection P1.

[Each Injection and Combustion Area]

The ideal mode of the combustion inside the combustion chamber 6 is toperform the combustion with oxygen existing inside the combustionchamber 6 being used up. As described in this embodiment, inside thecombustion chamber 6 of which the bottom surface is defined by the crownsurface 50 having the first and second cavity parts 51 and 52 lined upin the two steps in the vertical direction, the pre-injection P1, themain injection P2, and the middle injection P3 which were describedabove are performed in order to effectively utilize the oxygen existinginside the combustion chamber 6. For the effective use of the oxygeninside the combustion chamber 6, it is effective to separate thecombustion areas for the injections P1-P3 spatially and in time. Below,the combustion areas for the injections P1-P3 are illustrated withreference to FIGS. 10 to 13.

<Pre-Injection>

FIG. 10 is a view illustrating a situation of the fuel injection of thepre-injection P1 into the cavity 5C by the injector 15, and a flow ofthe mixture gas after the injection. FIG. 10 is a cross-sectional viewschematically illustrating the combustion chamber 6, and illustrates arelationship between the crown surface 50 (the cavity 5C) and theinjection axis AX of an injected fuel 15P1 injected from the injector15, and arrows F11, F12, F13, F21, F22, and F23 which schematicallyrepresent flows of the mixture gas after the injection.

The injector 15 is provided with the nozzle 151 disposed so as projectdownwardly toward the combustion chamber 6 from the combustion chamberceiling surface 6U (the lower surface of the cylinder head 4). Thenozzle 151 is provided with the injection hole 152 which injects fuelinto the combustion chamber 6. Although in FIG. 10 one injection hole152 is illustrated, a plurality of injection holes 152 are in factdisposed at equal pitch in the circumferential direction of the nozzle151. The fuel injected from the injection hole 152 is injected along theinjection axis AX in the figure. The injected fuel diffuses with a sprayangle θ. In FIG. 10, an upper diffusion axis AX1 illustrating thediffusion upward of the injection axis AX, and a lower diffusion axisAX2 illustrating the diffusion downward of the injection axis AX areillustrated. The spray angle θ is an angle formed by the upper diffusionaxis AX1 and the lower diffusion axis AX2.

In the pre-injection P1, the injector 15 injects fuel toward theconnecting part 53 of the cavity 5C. That is, the injection axis AX isdirected to the connecting part 53 by injecting fuel from the injectionhole 152 to the piston 5 at a given crank angle. FIG. 10 illustrates aspatial relationship between the injection axis AX and the cavity 5C atthe given crank angle. The fuel injected from the injection hole 152 isblown to collide the connecting part 53, while being mixed with airinside the combustion chamber 6 to form the mixture gas.

As illustrated in FIG. 10, the fuel 15P1 injected toward the connectingpart 53 along the injection axis AX collides the connecting part 53, andis then spatially divided into two parts comprised of a fuel portiongoing toward (downward) the first cavity part 51 (the arrow F11) and afuel portion going toward (upward) the second cavity part 52 (the arrowF21). That is, the fuel 15P1 injected while being directed to the centerpart 533 of the connecting part 53 is divided into the upper portion andthe lower portion, and, after that, the upper and lower portions flowalong the surface shapes of the first and second cavity parts 51 and 52,respectively, while being mixed with air existing in the cavity parts 51and 52.

In detail, the mixture gas which goes toward (downward) the arrow F11enters into the radially dented part 514 of the first cavity part 51from the lower end part 531 of the connecting part 53, and flowsdownwardly. Then, the mixture gas changes its flow direction fromdownward to an inward direction in the radial direction B by the curvedsurface shape of the radially dented part 514, and as illustrated by thearrow F12, flows along the bottom surface shape of the first cavity part51 having the first bottom part 512. At this time, the mixture gas ismixed with air inside the first cavity part 51 to be lower in theconcentration. Since the mountain part 54 exists, the bottom surface ofthe first cavity part 51 has a shape which rises toward the center inthe radial direction. Therefore, the mixture gas which flows in thearrow F12 direction is raised upwardly, and as illustrated by an arrowF13, it finally flows radially outwardly from the combustion chamberceiling surface 6U. Also, in such a flow, the mixture gas is mixed withair which remains inside the combustion chamber 6 to become ahomogeneous and leaner mixture gas.

On the other hand, the mixture gas which goes toward (upward) the arrowF21 enters into the taper area 524 of the second cavity part 52 from thethird upper end part 532 of the connecting part 53, and goes obliquelydownward along the inclination of the taper area 524. Then, asillustrated by the arrow F22, the mixture gas reaches the second bottompart 522. Here, the taper area 524 is a surface with an inclinationalong the injection axis AX (FIG. 3). Therefore, the mixture gas canflow smoothly in the radially outward direction. That is, the mixturegas can reach to a deeper position of the combustion chamber 6 in theradially outward direction due to the existence of the taper area 524and the existence of the second bottom part 522 located below the thirdupper end part 532 of the connecting part 53.

Then, the mixture gas is raised upwardly by the standup curved surfaceof the standing wall area 525 from the second bottom part 522, and flowsin the radially inward direction from the combustion chamber ceilingsurface 6U. In such a flow illustrated by the arrow F22, the mixture gasis mixed with air inside the second cavity part 52, and becomes thehomogeneous and leaner mixture gas. Here, since the standing wall area525 extending upwardly substantially in the vertical direction existsradially outward of the second bottom part 522, the injected fuel(mixture gas) is prevented from reaching the inner circumference wall ofthe cylinder 2 (in general, a liner (not illustrated) exists). That is,although the mixture gas can flow to near a location radially outward ofthe combustion chamber 6 because of the formation of the second bottompart 522, the interference with the inner circumference wall of thecylinder 2 is prevented by the existence of the standing wall area 525.Therefore, the cooling loss due to the interference can be reduced.

Here, the standing wall area 525 is provided with a shape in which alower part thereof is located inward of the upper end position thereofin the radial direction B. Therefore, the flow illustrated by the arrowF22 does not become excessively strong, and the mixture gas does notreturn overly inwardly in the radial direction B. If the flow of thearrow F22 is too strong, the mixture gas combusting in part collideswith newly injected fuel before the fuel is fully dispersed, and,therefore, the homogeneous combustion is impeded, which causes soot.However, the standing wall area 525 of this embodiment does not have theshape scooped out in the radially outward direction, and, therefore, theflow of the arrow F22 is restrained, and a flow which goes outward inthe radial direction B illustrated by the arrow F23 is also generated.Since the flow is pulled by a reverse squish flow in the later stage ofthe combustion, the flow of the arrow F23 is especially easy to begenerated. Therefore, the combustion in which a space radially outwardof the standing wall area 525 (a squish space on the peripheral flatsurface part 55) is also effectively utilized can be performed.

FIG. 11 is a cross-sectional view of the combustion chamber 6,illustrating primary areas where the premix combustion by thepre-injection P1 is generated. As described above, in the pre-injectionP1, the fuel 15P1 injected toward the connecting part 53 along theinjection axis AX collides with the connecting part 53 and is dividedspatially, and forms the mixture gas by being mixed with air (oxygen)existing in the respective spaces of the first and second cavity parts51 and 52, and then results in the combustion. Therefore, the combustionresulting from the pre-injection P1 is generated in a combustion area G1which uses oxygen existing in the space of the first cavity part 51, anda combustion area G2 which uses oxygen existing in the space of thesecond cavity part 52. Thus, the premix combustion by the pre-injectionP1 is performed after forming the homogeneous and leaner mixture gas bywidely utilizing the spaces of the first and second cavity parts 51 and52.

<Middle Injection>

FIG. 12 is a cross-sectional view of the combustion chamber 6,illustrating a primary area where the premix combustion by the middleinjection P3 is generated. In the middle injection P3, an area near theradial center of the combustion chamber 6, which is not used for thepremix combustion by the pre-injection P1 and the diffuse combustion bythe main injection P2 as will be described next, is a combustion areaG3. In the pre-injection P1, oxygen in the first and second cavity parts51 and 52 is utilized. On the other hand, in the main injection P2,oxygen which remains in the first cavity part 51 is utilized. Thesecombustions are both combustions which occur in an area other than nearthe radial center of the combustion chamber 6. On the other hand, in themiddle injection P3, oxygen in the radially center area of thecombustion chamber 6 which is not used for the pre-injection P1 and themain injection P2 is utilized positively to form and combust the mixturegas.

The middle injection P3 is an injection performed within a shorterinjection period (injection amount) than the pre-injection P1 and themain injection P2, and its penetration is small. Therefore, fuel 15P3injected along the injection axis AX by the middle injection P3 isdifficult to reach the first and second cavity parts 51 and 52 and,thus, it is mixed exclusively with air near the radial center of thecombustion chamber 6 to form the mixture gas, and creates the combustionarea G3. By providing such a combustion area G3, oxygen existing insidethe combustion chamber 6 can effectively be utilized, and a generationof soot, etc. can be reduced. Moreover, since the middle injection P3 isperformed at the timing between the pre-injection P1 and the maininjection P2 and creates the combustion area G3, the combustion by themiddle injection P3 contributes to the engine torque.

<Main Injection>

FIG. 13 is a cross-sectional view of the combustion chamber 6,illustrating a primary area where the diffuse combustion by the maininjection P2 is generated. The main injection P2 is an injectionperformed at a timing retarded from the pre-injection P1 where fuel isinjected toward the connecting part 53. In FIG. 6, one example where themain injection P2 is started near a TDC is illustrated. Moreover, thepenetration of the main injection P2 is large enough to reach the cavity5C. Therefore, fuel 15P2 injected along the injection axis AX by themain injection P2 is directed to a position slightly lower than theconnecting part 53, i.e., to an upper area of the first cavity part 51.The fuel 15P2 collides with the upper area, and as illustrated by anarrow F31, it flows along the bottom surface shape of the first cavitypart 51, and then, as illustrated by an arrow F32, it flows radiallyoutward from the combustion chamber ceiling surface 6U.

The main injection P2 is an injection in which the fuel (mixture gas)injected by the pre-injection P1 enters into the spaces of the first andsecond cavity parts 51 and 52, and is divided spatially, and, afterthen, a new mixture gas is formed by utilizing air which remains in thespace between the two portions of the divided mixture gas to create acombustion area G4. That is, the fuel of the pre-injection P1 firstinjected enters into the first and second cavity parts 51 and 52, and ismixed with air in the respective spaces to form the mixture gas, therebygenerating the combustion areas G1 and G2 (spatial separation).Therefore, immediately before the main injection P2 is started, unusedair (air which is not mixed with fuel) exists between the combustionareas G1 and G2. It can be said that the Egg Shape of the first cavitypart 51 contributes to such a formation of the unused air layer. Theinjected fuel of the main injection P2 enters into the space between thecombustion areas G1 and G2, and is mixed with unused air to form themixture gas. Then, the combustion area G4 by the diffuse combustion isformed by the mixture gas being given heat from the combustion areas G1and G2 by the previous pre-injection P1. This is the temporal separationof the fuel injection.

As described above, according to this embodiment, the injected fuel ofthe pre-injection P1 is divided spatially, and oxygen in the first andsecond cavity parts 51 and 52 is utilized. Moreover, the unused oxygenexisting between the combustion areas G1 and G2 generated by thepre-injection P1 is utilized by the injection separated in time (themain injection P2) to form the combustion area G4. Then, oxygen near theradial center of the combustion chamber 6 which is not utilized for thepre-injection P1 and the main injection P2 is utilized for the middleinjection P3 of which the penetration (injection period) is set in suchan unused area to form the combustion area G3. Therefore, the combustionwhich effectively utilizes oxygen existing inside the combustion chamber6 can be realized, thereby reducing the generation of soot.

[Control Flow]

FIG. 14 is a flowchart illustrating one example of a fuel injectioncontrol by the controller 70 (FIG. 5). The controller 70 acquiresvarious kinds of sensor values from the sensors SN1-SN12 illustrated inFIG. 5 and other sensors (an in-cylinder-pressure sensor, etc.) at everygiven sampling cycle (Step S1). Therefore, information related to anoperating range of the vehicle (the operating condition of the enginebody 1) and environment information used as the combustion environmentalfactor (described below) are acquired. The operating conditiondetermining module 73 determines, with reference to this information,whether the current operating range corresponds to the PCI range inwhich the premixed compression ignition combustion is to be performed.Here, a flowchart under a condition of being in the PCI range isillustrated.

Next, the target torque setting module 71 sets a target engine torquebased on the accelerator opening detected by accelerator opening sensorSN10 (Step S2; target torque setting step). In response to this, theinjection amount setting module 74 sets an injection amount of fuel tobe supplied into the combustion chamber 6 from the injector 15 per onecycle (a cycle comprised of intake, compression, expansion, and exhauststroke). The injection amount setting is a target injection amount toachieve the target torque (Step S3; fuel injection amount determiningstep).

Then, the injection pattern setting module 75 reads the setting map ofthe preset injection pattern for every target injection amount set atStep S3 (the combination of the engine speed and the engine load) fromthe memory 78, and sets the injection pattern according to the targetinjection amount (Step S4; injection pattern setting step). Thisinjection pattern is a pattern including the pre-injection P1, the maininjection P2, and the middle injection P3, where the pre-injection P1and the main injection P2 are such that the pressure waves generated bythe combustions caused by the injections cancel each other out.Moreover, a part of the injection amount originally to be assigned tothe pre-injection P1 and the main injection P2 is reduced whilemaintaining the injection amount ratio of the injections P1 and P2, andthe reduced amount is assigned to the middle injection P3.

Although various techniques are employable as this assignment, forexample, injection parts on the end timing CA2 side and the end timingCA6 side (refer to FIG. 9) of the pre-injection P1 and the maininjection P2 are reduced (shortening the tail end sides of the injectionperiods), and the reduced amounts are assigned to the middle injectionP3. Moreover, the phrase “maintaining the injection amount ratio” asused herein refers to setting the following injection amount ratio. Whenthe injection amount ratio of the injection amounts assigned to thepre-injection P1 and the main injection P2 is

P1:P2=5:4,

the injection amounts of both the injection P1 and P2 are reducedequally by 10%, for example (the relationship of P2=0.8×P1 ismaintained), and these reduced parts are assigned to the middleinjection P3 to set the injection amount ratio as

P1:P2:P3=4.5:3.6:0.9.

Note that at Step S4, the injection pattern setting module 75 may setthe injection pattern by calculating it each time according to thetarget injection amount, without depending on the setting map.

Then, the estimating module 76 estimates an occurring timing of the peakof the heat release rate of the premix combustion based on theenvironment information (the combustion environmental factor) acquiredat Step S1 by using the estimation model equation stored in the memory78. Here, the occurring timing is evaluated based on a “peak delay”which means a delay time of the peak of the heat release rate of thepremix combustion (the earlier-stage peak HAp) appears after startingthe pre-injection P1 (the start timing CA1). Further, the estimatingmodule 76 compares the estimated peak delay with a target peak delaywhen the combustion environmental factor is within a standard range toobtain an offset between the estimation and the target (Step S5).

Here, description is added for the combustion environmental factor. Theprimary combustion environmental factors which affect the controllingamounts inside the combustion chamber 6 include a wall surfacetemperature of the cylinder block 3, an in-cylinder pressure, anin-cylinder temperature, an in-cylinder oxygen concentration, an enginespeed (load), a fuel injection amount, a fuel injection timing, and afuel injection pressure. For example, the wall surface temperature, thein-cylinder pressure, and the in-cylinder temperature vary with anambient temperature, an ambient pressure, and an engine cooling watertemperature. Moreover, the in-cylinder oxygen concentration varies withan EGR gas amount taken into the combustion chamber 6. Moreover, thecombustion environmental factors may also vary according to transitionalfactors when the operating condition changes largely (when the intakeair temperature and the supercharging pressure are deviatedtransitionally).

FIGS. 15A to 15C are view illustrating a model equation to estimate theoccurring timing of the earlier-stage peak HAp of the earlier-stagecombustion portion HA in the heat release rate characteristic H. Asillustrated in FIG. 15A, the occurring timing of the earlier-stage peakHAp is estimated by the “peak delay.” Like this embodiment, when thefuel injection is divided into the pre-injection P1, the main injectionP2, and the middle injection P3, the ignition timing is determinedaccording to the executing situation of the pre-injection P1 whichinjects a comparatively larger amount of fuel at the earliest timing.When the mode of the pre-injection P1 is determined, the combustionaccompanying the main injection P2 becomes combustion which iscomparatively high in robustness. Therefore, the earlier-stage peak HAp(ignition timing) is used as the target for the adjustment.

FIG. 15B illustrates the estimation model equation of the peak delayused by the estimating module 76. Here, the characteristic of eachfactor is expressed by the Arrhenius type estimation equation. Theright-hand side of the equation includes items, such as a coefficient A,the fuel injection amount, the fuel injection timing, the fuel injectionpressure, the in-cylinder pressure, the in-cylinder temperature, thewall surface temperature, the in-cylinder oxygen concentration, and theengine speed. The coefficient A is an intercept which entirely variesthe value of the right-hand side. Indexes B to I given to the items ofthe right-hand side illustrate the sensitivities of the items, where thepositive sign indicates proportionality and the negative sign indicatesan inverse proportion. Note that an engine oil temperature may also beadded as the item.

FIG. 15C is a table illustrating a calibration result of the estimationmodel equation, where the value of the coefficient A, and the values ofthe indexes B to I are illustrated. This result is such that theparameters related to the injection, such as the fuel injection amount,the fuel injection timing, and the fuel injection pressure, are fixed toreference values corresponding to the target heat release ratecharacteristic, and a large amount of data is acquired by changing thecontrolling amounts, such as the ambient temperature, the ambientpressure, then engine cooling water temperature, and the EGR gas amountand a variation in the combustion state (the rate of heat release) andthe in-cylinder state variation are associated with each other by amultiple linear regression analysis. It is confirmed that a differencebetween the estimation result of the “peak delay” by the estimationmodel equation (the crank angle at which the earlier-stage peak HApoccurs) and the “peak delay” by the actual measurement is ±2 deg. orless.

Next, the correcting module 77 derives a correction value to correct thefuel injection timing of the pre-injection P1 set at Step S4 so that theoffset obtained at Step S5 is corrected (Step S6). That is, a fuelinjection timing of the pre-injection P1 to be able to cause theearlier-stage peak HAp to appear at a target timing is derived. When theoccurring timing of the peak of the earlier-stage peak HAp is estimatedto be late with respect to the target occurring timing, the start timingCA1 of the pre-injection is corrected to be advanced, and, on the otherhand, when it is estimated to be early, the start timing CA1 iscorrected to be retarded. Of course, if the combustion environmentalfactor is within a preset center range where the correction is notnecessary, the correction by the correcting module 77 will not beperformed. Note that as for the main injection P2 and the middleinjection P3, both are the diffuse combustions, and, therefore, sincethe peak delays hardly occur, the changes in the fuel injection timingsare not necessary.

Then, the injection pattern setting module 75 corrects the executiontiming of the pre-injection P1 with reference to the correction valueacquired at Step S6, and then sets the final values of the fuelinjection amounts and the fuel injection timings for the pre-injectionP1, the main injection P2, and the middle injection P3. Then, the fuelinjection controlling module 72 controls the injector 15 as the settingto perform the fuel injection (Step S7).

[Operation & Effects]

According to the control device for the engine according to thisembodiment described above, the fuel injected by the pre-injection P1(first injection) toward the connecting part 53 of the cavity 5C entersinto the first and second cavity parts 51 and 52, and is mixed with air(oxygen) in the cavity parts 51 and 52 to form the mixture gas, therebyresulting in the premix combustion. Moreover, the fuel injected by themain injection P2 (second injection) which is performed at the retardedtiming from the pre-injection P1 is mixed with air which remains in thefirst cavity part 51 to form the mixture gas, thereby resulting in thediffuse combustion. Then, in the middle injection P3 performed at thetiming between the pre-injection P1 and the main injection P2, the fuelis injected during the injection period shorter than the pre-injectionP1 and the main injection P2.

The fuel injected by the middle injection P3 during the short injectionperiod becomes difficult to reach the first and second cavity parts 51and 52, and is mixed with air exclusively near the radial center of thecombustion chamber 6 to form the mixture gas, thereby resulting in thecombustion. That is, in the middle injection P3, oxygen in the radiallycenter area of the combustion chamber 6 which is not used for thepre-injection P1 and the main injection P2 is utilized positively toform the mixture gas. Thus, the oxygen existing inside the combustionchamber 6 can effectively be utilized, and, therefore, the generation ofsoot can be reduced. Moreover, since the middle injection P3 isperformed at the timing between the pre-injection P1 and the maininjection P2, the combustion by the middle injection P3 contributes tothe engine torque.

[Modifications]

As described above, although the embodiment of the present disclosure isdescribed, the present disclosure is not limited to this configuration.For example, in the above embodiment the example in which thepre-injection P1, the main injection P2, and the middle injection P3 areperformed as the fuel injection pattern is illustrated. This is merelyan example and may additionally be provided with another injection. Forexample, after the main injection P2, a post injection may be performedaiming at a further reduction of soot. Moreover, although in the aboveembodiment the example in which the pre-injection P1 and the middleinjection P3 are each performed by one injection is described, eachinjection may be performed by 2 times or more injections which dividethe assigned injection amount.

It should be understood that the embodiments herein are illustrative andnot restrictive, since the scope of the invention is defined by theappended claims rather than by the description preceding them, and allchanges that fall within metes and bounds of the claims, or equivalenceof such metes and bounds thereof, are therefore intended to be embracedby the claims.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1 Engine Body    -   Cylinder    -   Piston    -   Crown Surface    -   5C Cavity    -   First Cavity Part    -   Second Cavity Part    -   Connecting Part    -   Combustion Chamber    -   6U Combustion Chamber Ceiling Surface (Ceiling Surface)    -   Injector (Fuel Injection Valve)    -   Controller (Control Device For Engine)    -   Target Torque Setting Module (Target Torque Setting Step)    -   Fuel Injection Controlling Module    -   P1 Pre-Injection (First Injection)    -   P2 Main Injection (Second Injection)    -   P3 Middle Injection    -   EAw Earlier-Stage Pressure Wave (First Pressure Wave)    -   EBw Later-Stage Pressure Wave (Second Pressure Wave)    -   R1, R2, R3 First Portion, Second Portion, Third Portion

What is claimed is:
 1. A control device for an engine including acombustion chamber formed by a cylinder, a crown surface of a piston,and a ceiling surface, and a fuel injection valve disposed in a radiallycenter part of the ceiling surface and configured to inject fuel intothe combustion chamber, a cavity being formed in the crown surface ofthe piston, the cavity including a first cavity part disposed in aradially center area of the crown surface and provided with a firstbottom part having a first depth in a cylinder axis direction; a secondcavity part disposed in the crown surface at a location radially outwardof the first cavity part and provided with a second bottom part having asecond depth shallower than the first depth in the cylinder axisdirection; and a connecting part connecting the first cavity part withthe second cavity part, the control device comprising: a processorconfigured to execute a fuel injection controlling module to controloperation of the fuel injection valve, wherein the fuel injectioncontrolling module causes the fuel injection valve to perform: a firstinjection in which fuel is injected at a timing when the piston islocated at an advancing side of a compression top dead center, and aninjection axis of the fuel injection valve intersects with theconnecting part of the cavity; a second injection in which fuel isinjected toward the first cavity part at a retarding side of the firstinjection; and a middle injection in which fuel is injected at a timingbetween the first injection and the second injection, for an injectionperiod shorter than each of the first injection and the secondinjection.
 2. The control device of claim 1, wherein the fuel injectioncontrolling module sets the injection period so that an injectiondistance of the middle injection becomes shorter than a distance betweenan injection hole of the fuel injection valve and a wall surface of thecavity.
 3. The control device of claim 1, wherein the fuel injectioncontrolling module sets a fuel amount injected in the first injectionlarger than a fuel amount injected in the second injection.
 4. Thecontrol device of claim 1, wherein the fuel injection controlling modulesets a start timing of the middle injection at a timing closer to astart timing of the second injection than an end timing of the firstinjection.
 5. The control device of claim 1, wherein the fuel injectioncontrolling module sets the injection period of the second injection sothat a start timing of the second injection becomes closer to thecompression top dead center than an end timing of the second injection.6. The control device of claim 1, wherein the fuel injection controllingmodule causes the fuel injection valve to perform the first injectionand the second injection so that a first pressure wave resulting fromcombustion by the first injection and a second pressure wave resultingfrom combustion by the second injection appear with a half-cycle offset.7. An engine, comprising: a combustion chamber formed by a cylinder, acrown surface of a piston, and a ceiling surface; a fuel injection valvedisposed in a radially center part of the ceiling surface and configuredto inject fuel into the combustion chamber; a cavity formed in the crownsurface of the piston, the cavity including: a first cavity partdisposed in a radially center area of the crown surface and providedwith a first bottom part having a first depth in a cylinder axisdirection; a second cavity part disposed in the crown surface at alocation radially outward of the first cavity part and provided with asecond bottom part having a second depth shallower than the first depthin the cylinder axis direction; and a connecting part connecting thefirst cavity part with the second cavity part; and a control deviceincluding a processor configured to execute a fuel injection controllingmodule to control operation of the fuel injection valve, wherein thefuel injection controlling module causes the fuel injection valve toperform: a first injection in which fuel is injected at a timing whenthe piston is located at an advancing side of a compression top deadcenter, and an injection axis of the fuel injection valve intersectswith the connecting part of the cavity; a second injection in which fuelis injected toward the first cavity part at a retarding side of thefirst injection; and a middle injection in which fuel is injected at atiming between the first injection and the second injection, for aninjection period shorter than each of the first injection and the secondinjection, wherein the first cavity part includes, in a cross-sectionincluding a cylinder axis, a first portion of an arc shape furthest fromthe fuel injection valve, a second portion of the arc shape locatedbetween the first portion and the connecting part, and a third portionof the arc shape extending radially inward from the first portion, andwherein a radius of curvature of the arc shape decreases from the secondportion to the first portion, and increases from the first portion tothe third portion.